1. Field of the Invention
The present invention relates to a method of forming an organic semiconductor pattern and a method of manufacturing an organic thin film transistor (TFT) using the method of forming the organic semiconductor pattern. More particularly, the present invention relates to a method of forming an organic semiconductor pattern to simplify a manufacturing process and a method of manufacturing an organic thin film transistor (TFT) using the method of forming the organic semiconductor pattern.
2. Description of the Related Art
A flat panel display device has advantageous characteristics such as being thinner, having a lighter weight, and being of a smaller size than a cathode ray tube display device. Flat panel display devices include a liquid crystal display (LCD) devices, field emission display (FED) devices, a plasma display panel (PDP) display device, and an electro-luminescence (EL) display device. The flat panel display device has been developed to improve an image display quality and to increase a screen size.
The PDP display device has a simple manufacturing process and a large screen. However, the PDP display device has higher power consumption than the LCD device. The LCD device of an active matrix type, which has a thin film transistor (TFT), is manufactured using a semiconductor manufacturing process. An electronic device such as a notebook computer, a television receiver, a mobile communication device, and similar items include an LCD device. However, typically the screen size of the LCD device is small, and the power consumption of a backlight assembly of the LCD device is high. In addition, an LCD device includes optical elements such as a polarizer, a prism sheet, and a diffusion plate, so that a luminance and a viewing angle of the LCD device are decreased. EL display devices are divided into two categories, an inorganic EL display device and an organic light emitting display (OLED) device. The inorganic EL display device includes an inorganic light emitting material. The OLED device includes an organic light emitting material. The EL display device is a light emissive type display device so that the response speed, luminance and viewing angle of the EL display device are greater than those of a light non-emissive type display device such as an LCD device.
A flexible display device of a high image display quality has been devised for mobile electronic devices. The flexible display device typically includes a display element having a low manufacturing cost, high flexibility, and high endurance. The display element of the flexible display device includes an organic semiconductor material. The organic semiconductor material includes polyacetylene that is a conjugate organic polymer, polyphenylenes, end-substituted thiophene oligomers, pentacent, phthalocyanine, and regioregularpoly(3-alkylthiophene)s.
The manufacturing processes used in making flexible display devices include a patterning process of the organic semiconductor material. The organic semiconductor material is easily molded to have a fiber shape or a film shape. The organic semiconductor material has various characteristics such as flexibility, electrical conductivity, and low manufacturing cost, so that an electric element or a photo element includes the organic semiconductor material.
Organic TFTs including the organic semiconductor material were developed in 1980s. An organic TFT has substantially the same structure as a silicon TFT, except for the channel layer which includes the organic semiconductor material. The organic TFT has a simpler structure and a lower manufacturing cost than a silicon TFTs. A Π-conjugated organic material has been used for the channel layer of the organic TFT. However, the Π-conjugated organic material has poor electrical characteristics. An organic TFT using the Π-conjugated organic material is not manufactured by a mass production, and is not resistant to oxygen and moisture, thereby decreasing the lifetime of the organic TFT.
The manufacturing process used to make an organic TFT includes a polymer semiconductor process and an organic semiconductor process. The polymer semiconductor process includes a high polymer as a semiconductor material. The semiconductor material used in the high polymer is dissolved in a solvent, and the dissolved semiconductor material is coated on a substrate using a spin coating method. The organic semiconductor process utilizes a low polymer as a semiconductor material. The semiconductor material used in the low polymer process is not dissolved in a solvent. The semiconductor material used in the low polymer includes a pentacene. Formula 1 represents a pentacene molecule which is an aromatic hydrocarbon having five benzene rings.

The pentacene molecule includes a plurality of single bonds and a plurality of double bonds so that an electron mobility in each of the pentacene molecules is high. However, electrons mobility between adjacent pentacene molecules through hopping so that an electron mobility out of the pentacene molecules is changed with respect to a degree of close-packing of the pentacene molecules. When the pentacene molecules are deposited in a vacuum, the pentancene molecules have high field effect mobility of the electrons (Synthetic metals, 41-43, 1127 (1991)). A precursor of the pentacene molecules dissolved in a solvent is coated to form the semiconductor layer. However, when the semiconductor layer is formed by the dissolved pentacene molecules, the characteristics of the semiconductor layer are deteriorated, and the dissolved pentancene molecules are heated at a high temperature of about 140° C. to about 180° C.
The organic semiconductor material is deposited on the substrate using a shadow mask. When the organic semiconductor material is deposited using a shadow mask, an etching process is unnecessary. However, shadow masks are not easily prepared.
For example, the thickness of the shadow mask is small and accordingly it is not easily handled. The shadow mask makes contact with the substrate during the deposition process so that the shadow mask is damaged during the deposition process, and a cleaning process is required for the shadow mask. Also, the shadow mask is not suitable for a large substrate. In addition, the shadow mask is expensive which, in turn, increases the manufacturing cost of the organic TFT.